The markets: Civil infrastructure (2018)

According to a report by the coalition Transportation for America (Washington, DC, US), titled The Fix We’re In For: The State of our Nation’s Busiest Bridges, there are 69,223 structurally deficient highway bridges in the U.S. alone — 11.5% of all US highway bridges — that require rehabilitation or replacement.

Aging infrastructure offers a potentially huge market for composite materials. According to a report by the coalition Transportation for America (Washington, DC, US), titled The Fix We’re In For: The State of our Nation’s Busiest Bridges, there are 69,223 structurally deficient highway bridges in the U.S. alone — 11.5% of all US highway bridges — that require rehabilitation or replacement. These numbers have encouraged development of a number of composites-enabled technologies. 

The early deterioration of concrete due to the corrosion and failure of steel rebar has been well documented. Conventional repairs could cost billions. In many locales, the useful life of corrosion-prone steel-rebar-reinforced concrete is limited to 25 years, rather than the 75-100 years once promised by its advocates. Therefore, the lifecycle cost advantages, not to mention the safety benefits, of using composite rebar continue to overcome resistance among change-averse municipalities. 

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That said, progress is still hit-and-miss. Faced with limited annual budgets, state and local transportation executives, particularly in the US, have the choice to replace a certain number of bridges with concrete that could last 30-40 years at best, or half as many using composites that could last up to 100 years. 

Despite somewhat dashed early hopes for composite bridge adoption in the US and the continuing reticence of permitting authorities, the critical need for bridge designs that can resist corrosion and extend useful lifecycles could yet turn the tide. Projects still make the news, particularly in pedestrian bridges. A case in point, one that illustrates how well composites can “fill the bill” in every practical respect, came to CW’s attention in 2017. The Mountains-to-Sea Trail, the longest footpath in the US state of North Carolina, passes through 37 counties as it winds down from the Appalachian Mountains to the Outer Banks islands. Near the town of Blowing Rock, however, hikers had to wade across Boone Fork Creek, which was dangerous during high water flows. Funds were secured to build a bridge, but the building process presented serious negatives. Because the crossing point is in a remote US National Forest location with no vehicular access, conventional bridge-building methods, which require cranes and trucks to move metal trusses or concrete, weren’t feasible. Charged with responsibility for the bridge’s design and its construction supervision, Arete Engineers LLC (Boone, NC, US) knew that a lightweight, easily transported and assembled solution was needed. Arete’s primary engineer, T. Shawn Ausel, P.E., was familiar with pultruder Strongwell (Bristol, VA, US) and specified composite structural elements that, much lighter than steel or concrete, could be ferried by helicopter to a drop site close to the build site.

The 1.2m-wide by 25m-long bridge structure was constructed from EXTREN 525 pultruded fiberglass structural profiles wet out with UV-resistant polyester modified with fire-retardant additives. EXTREN components include a surface veil to prevent glass fibers from penetrating the resin surface and to enhance bridge corrosion and UV resistance. The profiles — 20-cm wide channels and 50-mm by 50-mm pultruded tubes — were pigmented olive green to better blend with the forest setting (paint on steel or concrete wouldn’t last). Strongwell’s pultruded fiberglass SAFDECK 60-cm wide panels, also produced with fire-retardant polyester but then coated with an epoxy grit, were specified for the pedestrian deck surface.

In Europe, those responsible for replacing civil infrastructure have taken more readily to composites. Infrastructure composites specialist FiberCore Europe (Rotterdam, The Netherlands), for one example, has fabricated and installed more than 500 composite bridge structures since 2008, as well as lock gates for shipping canals. 

 

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